The goal of this proposal is to address the limitations of clinically employed photosensitizing drugs in photodynamic therapy (PDT). Novel two-photon absorbing dendrimer photosensitizers are described that are capable of generating singlet oxygen by irradiation with 780 nm light and could allow PDT for treatment of previously inaccessible subcutaneous tumors. The preparation of photosensitizing dendrimer-polymer hybrids are also described as a means to increase the efficacy of the photosenzitizer. Additional elements of novelty included in this proposal include the incorporation of a "pH safety switch" into the dendrimer that is governed by photoinduced electron transfer, and the development of new core molecules that should allow for the preparation of a variety of multidomain dendrimers. [unreadable] [unreadable] [unreadable]